Taking climate change seriously on the Colorado River: a practical step

Preparing for climate change on the Colorado River is hard. But we will make it harder, and narrow the scope of our options for dealing with it, if we don’t incorporate realistic flow reduction scenarios in our planning efforts.

That’s the thrust of an editorial Brad Udall and I have in this week’s issue of the journal Science:

In the 1920s, E. C. LaRue, a hydrologist at the United States Geological Survey, did an analysis of the Colorado River Basin that revealed the river could not reliably meet future water demands. No one heeded his warning. One hundred years later, water flow through the Colorado River is down by 20% and the basin’s Lake Powell and Lake Mead—the nation’s two largest reservoirs—are projected to be only 29% full by 2023. This river system, upon which 40 million North Americans in the United States and Mexico depend, is in trouble. But there is an opportunity to manage this crisis. Water allocation agreements from 2007 and 2019, designed to deal with a shrinking river, will be renegotiated over the next 4 years. Will decision-makers and politicians follow the science?

The editorial draws on Brad’s work on Colorado River Basin climate change hydrology and my work, with Eric Kuhn, on the history of the use of science in decision making.

Brad and I see a risk that looks an awful lot like the situation a century ago that Eric and I sussed out in Science Be Dammed.

Then, it was the temptation to use overly optimistic flow estimates as the basis for the Colorado River Compact and the decisions that followed, creating the overallocation of the river that we struggled with now. Today, it is the risk that we will fall back on the already-low 20th century hydrology as a baseline for the modeling done in support of the renegotiation of the Colorado River management guidelines. That hydrology, as all of us know, is bad. But the latest climate science suggests we need to have plans in place to deal with worse:

As the basin’s water management community prepares for a new round of negotiations over the water allocation rules, how bad of a “worst case scenario” should be considered and who will get less water as a result? It is tempting to use today’s 20% flow decline as the new baseline—that is, modeling future reductions on the basis of what has already been observed. But only by planning for even greater declines can we manage the real economic, social, and environmental risks of running low on a critical resource upon which 40 million North Americans depend.

Our thanks to the editorial staff at Science for their interest and help with the piece.




  1. Why are the decision makers waiting for more decline in the reserves before acting?

    The word “science” has become a pejorative in today’s political world. In any case, the norm is to disregard science in favor of financial/political concerns. It doesn’t take a PHD to see there is a giant problem. You can do the math on an envelope.

    Using words like “risks” and “hopes” only encourage procrastination. We are past that. We are currently in the “worst case scenario” for the purpose of reallocation. If the world reverses and the area gets wet again then WHOOPEE!

    Fill the reservoirs back up. No problem.

  2. The issue is systemic. Here in Arizona, we are being told that shortages are coming, but our groundwater situation is fine. Except that, as Kathleen Ferris and Sarah Porter point out – https://morrisoninstitute.asu.edu/myth_of_safe_yield – it is not. Perpetual growth is the economic model and those who cannot get in on the action are trying to change laws so that they can.

    It is very depressing.

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